1. Field of the Invention
The invention relates to controlling the motion of an object and in particular to following a planned path.
2. Related Art
Many methods of control are known. These typically provide feedback from sensors to adjust the actuators in a controlled machine. A common method is called a PID (because it contains proportional, integration and derivative terms), such as on pages 379-392 in the reference of Modern Control Systems by Richard C. Doff, Addison-Wesley Publishing Company, Third Edition, 1983, where the actuator responds in proportion to the error between the sensed values or position and the desired values or position. A desired trajectory, typically described by an elementary motion and optionally including velocity and possibly acceleration is the sequence of desired task states for the device to follow. Elementary motions are usually those that can be expressed in simple mathematical terms. The expression is usually simple because the computation is repeated in a feedback loop. A more mathematically complex motion is also possible, but only if there is sufficient time in the feedback loop. Examples of simple motions are arcs or straight lines. While sensing, the calculation of the error in sensed parameters (or parameters derived from them) and generating the corrective action for the actuator is called servoing. The sensed parameters are typically whatever characteristics are being monitored such as the position, orientation, velocity, or acceleration. Some parameters can be derived. For example, velocity can be determined given two positions and knowing the elapsed time. Elapsed time is commonly available on real time clock chips on many microprocessors. The servo process usually has a setpoint which is a desired final destination often defined by a final location, orientation, and possibly velocity and orientation.
The maneuvers of a controlled vehicle, such as a car, are defined by the direction arrows in a configuration space. Ordinarily, a path is read out of the configuration space and then set points are sent to the vehicle. Although this works, improvements to the control is needed to produce a smoother motion which also allows for better automatic recovery from interferences.